I'd say Yamamoto, because his dad's death affected him in so much ways that he is not as happy-go-lucky as before.
But I wanted to say that Fuuta was the one that changed the most. He wasn't a little kid anymore and he got taller, way taller than Tsuna. He also got quieter, and he does not have the book w/ him, instead, he have a laptop-ish item. and he doesn't have his scarf anymore

I'd say Yamamoto, because his dad's death affected him in so much ways that he is not as happy-go-lucky as before.
But I wanted to say that Fuuta was the one that changed the most. He wasn't a little kid anymore and he got taller, way taller than Tsuna. He also got quieter, and he does not have the book w/ him, instead, he have a laptop-ish item. and he doesn't have his scarf anymore

One thing we hated about Fuuta changed in ten years is that, his voice did not really 'mature' at all.

I'd say Yamamoto, because his dad's death affected him in so much ways that he is not as happy-go-lucky as before.
But I wanted to say that Fuuta was the one that changed the most. He wasn't a little kid anymore and he got taller, way taller than Tsuna. He also got quieter, and he does not have the book w/ him, instead, he have a laptop-ish item. and he doesn't have his scarf anymore

One thing we hated about Fuuta changed in ten years is that, his voice did not really 'mature' at all.

I'd say Yamamoto, because his dad's death affected him in so much ways that he is not as happy-go-lucky as before.
But I wanted to say that Fuuta was the one that changed the most. He wasn't a little kid anymore and he got taller, way taller than Tsuna. He also got quieter, and he does not have the book w/ him, instead, he have a laptop-ish item. and he doesn't have his scarf anymore

One thing we hated about Fuuta changed in ten years is that, his voice did not really 'mature' at all.